Conductive particle, anisotropic conductive interconnection material that uses the conductive particle, and method for producing the conductive particle

ABSTRACT

There is disclosed a conductive particle used for an anisotropic conductive connection material for establishing conductive interconnection between e.g. a substrate and an electrical component. The conductive particle includes a base particle ( 2 ) exhibiting electrical conductivity at least on its surface and a continuous insulating resin film ( 3 ) formed by welding of fine particles ( 3   a ) of an insulating resin that composes the resin film. The surface of the base particle is coated with the continuous insulating resin film. There are formed voids at least between neighboring fine particles.

TECHNICAL FIELD

This invention relates to a conductive particle used in an anisotropicconductive interconnection material that electrically interconnects asubstrate and electronic parts, and the anisotropic conductiveinterconnection material that uses the conductive particle. Thisinvention also relates to a method for producing the conductiveparticle.

The present application claims priority rights based on the JapanesePatent Application 2007-107475, filed in Japan on Apr. 16, 2007. Thetotal disclosure of this patent application of the senior filing date isto be incorporated herein by reference.

BACKGROUND ART

In related art, to interconnect a connection terminal of a semiconductordevice and a connection terminal of a substrate, on which to mount thesemiconductor device, the practice has been to interconnect the twoconnection terminals by anisotropic conductive interconnection with theuse of an anisotropic conductive interconnection material. With suchanisotropic conductive interconnection, a film-like or paste-likeanisotropic conductive connection material, obtained on dispersing fineconductive particles in an insulating adhesive, is sandwiched betweenthe two materials to be connected. The resulting assembly is heated andpressured to bond the two materials and the connection material togetheras electrical conductivity is maintained.

Recently, with the tendency towards miniaturization and higherperformance of semiconductor devices, as exemplified by a liquid crystaldisplay device, miniaturization of circuits as to be used theanisotropic conductive interconnection is progressing. To cope withthis, a strong demand is presented for fine pitch between the circuits,while there is felt a strong concern as to the tendency to shortingwhich may be produced on setting up the anisotropic conductiveinterconnection. To meet this general demand for the fine pitch, aconductive particle 101 made up of a conductive particle 102, used as ananisotropic conductive interconnection material, and an insulating resinfilm 103, coated on the particle 102, as shown in FIG. 1, has come to beused to show two functions that are contrary to each other, namely theelectrical conductivity and the insulating properties.

However, as the pitch becomes finer, there is presented a problem that,with a conventional insulating film uniformly coated on a conductiveparticle, if the film thickness is increased to assure the insulatingproperties between neighboring circuit components, the electricalconductivity is lowered due to the aforementioned characteristics actingin contrary fashion to each other, namely the insulating properties andthe electrical conductivity.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention provides a conductive particle useful forimproving interconnection reliability even with narrow-pitch bumps, aconductive particle, an anisotropic conductive interconnection materialemploying the conductive particle, and a method for producing theconductive particle.

A conductive particle according to an embodiment of the presentinvention includes a base particle exhibiting electrical conductivity atleast on its surface, and a continuous insulating resin film that coversthe surface of the base particle. The resin film is formed by welding offine particles of the insulating resin. There are formed voids at leastbetween neighboring fine particles.

An anisotropic conductive connection material of an embodiment of thepresent invention includes larger numbers of the conductive particlesdispersed in an insulating adhesive.

A method for producing a conductive particle according to an embodimentof the present invention includes coating a surface of a base particlewith an insulating resin film by colliding fine particles of theinsulating resin to the surface of the base particle to cause adhesionof the fine particles to the surface of the base particle. At least thesurface of the base particle exhibits the electrical conductivity. Theinsulating resin of the fine particle is selected from the groupconsisting of a cross-linked acrylic resin, a styrene-acryl copolymer, adivinylbenzene-acryl copolymer, a styrene-divinylbenzene copolymer, amelamine-formaldehyde copolymer, a silicone-acryl copolymer, apolyamide, a polyimide, polybutadiene and NBR.

A method for producing a conductive particle according to anotherembodiment of the present invention includes a first step of forming aninsulating resin film presenting larger numbers of voids in an initialstate by collision fine particles of an insulating resin to a surface ofa base particle. At least the surface of the base particle exhibits theelectrical conductivity. The method of the present invention alsoincludes a second step of continuing the collision of the fine particlesto such an extent that the voids on a surface of the insulating resinfilm are decreased and the voids towards the base particle aremaintained.

The conductive particle according to another embodiment of the presentinvention includes a continuous insulating resin film that coats thebase particle exhibiting the electrical conductivity. The insulatingresin film is formed by welding of the fine particles of the insulatingresin. There are formed preset voids between neighboring fine particlesto assure the insulating properties between bumps. The insulating resinfilm on the outer shell may readily be cracked to assure facilitatedreliable interconnection performance and high connection reliabilityeven with narrow-pitch bumps.

With the anisotropic conductive interconnection material according toanother embodiment of the present invention, high connection reliabilityis realized because the conductive particles that assure facilitatedreliable interconnection performance even with narrow-pitch bumps aredispersed in an insulating adhesive.

With the method for producing the conductive particle, according toanother embodiment of the present invention, it is possible to prepare aconductive particle having preset voids within the bulk of an insulatingresin film that coats a base particle, such as to assure facilitatedreliable interconnection performance and high interconnectionreliability even with narrow-pitch bumps.

Other objects and advantages of the present invention will becomeapparent from the following description of its preferred embodimentswhich will now be made with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a conductive particle inrelated art.

FIG. 2 is a cross-sectional view showing a conductive particle accordingto an embodiment of the present invention.

FIGS. 3A to 3C are cross-sectional views for illustrating various stepsof a method for producing the conductive particle according to anembodiment of the present invention. FIG. 3A shows a conductive particlewith an insulating film in a state in which the processing forhybridization has been continued beyond a state of production by themethod of the present invention for the sake of comparison with thepresent invention. FIG. 3B shows a conductive particle with aninsulating film in a state in which the particle has been produced bythe method of the present invention, that is, a state in which thesecond step of the method of the present invention has been finished.FIG. 3C shows a conductive particle with an insulating film in a statein which the first step of the inventive method has been finished.

FIG. 4 is a schematic view schematically showing an IC chip forevaluation used for evaluating the conductive particles according to theExamples and those according to Comparative Examples.

FIG. 5 is a schematic view schematically showing a glass substrate andan IC chip used for evaluating the conductive particles according toExamples and Comparative Examples.

BEST MODE FOR CARRYING OUT THE INVENTION

A conductive particle carrying thereon an insulating film, according tothe present application, and an anisotropic conductive interconnectionmaterial that uses the conductive particle, carrying thereon aninsulating film, will now be described with reference to the drawings.

According to an embodiment of the present application, a conductiveparticle 1 carrying an insulating film thereon, is used in ananisotropic conductive interconnection material, such as an anisotropicconductive adhesive. According to an embodiment of the presentapplication, the anisotropic conductive adhesive as an anisotropicconductive interconnection material includes also an insulating adhesiveas a binder resin, into which are dispersed larger numbers of theconductive particles 1 each carrying the insulating film thereon. As theinsulating adhesive, thermosetting resins, such as epoxy or phenoxyresins, are preferably used. The present invention may also be appliedto an anisotropic conductive film (ACF) included by this anisotropicconductive adhesive on a release film.

Referring to FIG. 2, this conductive particle 1 carrying thereon aninsulating film, is made up of a conductive particle 2 used as a baseparticle, and an insulating resin film 3 is formed as a continuous filmby welding of fine particles 3 a of the insulating resin together,whereby the fine particles cover surface of the conductive particle. Theinsulating resin film 3 is sometimes referred to below as an outer shellinsulating layer. The continuous insulating resin film 3, formed bywelding the fine particles 3 a of the insulating resin, has largernumbers of voids A between neighboring ones of the fine particles 3 a todemonstrate both the insulating characteristic and the conductivecharacteristic of the conductive particle 1 carrying thereon theinsulating film. Each void A is a fraction of an interstice delimitedbetween a cube circumscribed to a sphere and the sphere. This fractionis a space left after 20 to 60% of the interstice were buried with thefine particles as a result of welding. The void ratio of the intersticebetween the cube and the sphere is approximately 47.64% (=100×(1−4/3×π×(½)³)), while the void ratio that is in a state that approximately20 to 60% of the interstice were buried with the fine particles is 19.1to 38.1%. It is noted that the void ratio shows the percentage of thecubic content of the void A based on 100% of the total cubic contentincluding the void A in the insulating resin film 3.

The conductive particle 1 carrying thereon an insulating film, is formedby causing the fine particles 3 a of the insulating resin to collide thesurface of the conductive particle 2 to deposit the fine particles onthe surface of the conductive particle 2 in a manner as later described.By so doing, the surface of the conductive particle 2 is coated by theinsulating resin film 3. When the conductive particle 2 is coated by theinsulating resin film 3 in this manner, the fine particles are depositedon the surface of the base particle so that a space is provided betweenthe neighboring fine particles such as to maintain the void ratio of theinsulating resin film 3 in a range of 19.1 to 38.1%. The insulatingresin film 3 is formed in such a manner that there is substantially novoid on its outer surface, which is thus smooth, while larger numbers ofvoids A are caused to exist on an inner surface of the insulating resinfilm 3, that is, the surface of the insulating resin film directing tothe base particle 2. In addition, the insulating resin film 3 is formedso that the amount of the voids A will decrease from the surface of thebase particle 2 along the film thickness, that is, so that the amount ofthe voids A2 on the outer side is smaller than that of voids A1 on theinner side. That is, the insulating resin film 3 is sparse towards itsinner side part, while being dense towards its outer side part includingits outer surface that forms its outer shell.

The conductive particle 2 has electrical conductivity at least in itsouter surface, and represents a base particle of the conductive particle1 carrying thereon an insulating film. The conductive particle 2 may,for example, be a particle of metal, such as gold, silver, platinum,nickel, copper, or a tin/nickel alloy, or a particle of resin, such asstyrene, divinylbenzene or benzoguanamine, as a nucleus, the surface ofwhich is plated with nickel or nickel/gold.

The conductive particle 2 is of a particle size of the order of 3 to 10μm, for example, is used. The fine particle 3 a of the insulating resinis of a particle size on the order of one-tenth of that of theconductive particle 2, and specifically on the order of 100 to 400 nm.The insulating resin film 3 formed by welding, has a thickness on theorder of, for example, 200 to 300 nm. The insulating resin film 3presents a substantially uniform outer surface, as a result of thewelding, with an inner surface of the insulating resin film 3 presentingthe voids between the neighboring fine particles, as described above.

The fine particles 3 a of the insulating resin that form the insulatingresin film 3 are solid particles. The fine particles 3 a of theinsulating resin are caused to collide the surface of the conductiveparticle 2 as the base particle so as to be deposited thereon, aspreviously mentioned. In addition, the voids A need to be formed in theinterior of the insulating resin film 3 such as to demonstrateconductive characteristic and insulating characteristic. To this end,solid particles are preferred to hollow particles. To prepare the fineparticles 3 a of the insulating resin, cross-linked acrylic resin, astyrene-acryl copolymer, a divinylbenzene-acryl copolymer, astyrene-divinylbenzene copolymer, a melamine-formaldehyde copolymer, asilicone-acryl copolymer, a polyamide, a polyimide, polybutadiene andNBR, for example, are used.

The properties of the particles used as the fine particles 3 a of theinsulating resin that form the insulating resin film 3, are selected insuch a manner that, when the particles are pressed by a heat press forten minutes under a condition of 100° C. and 2 MPa, the particles arefused together, and that, when the particles are pressed by the sameheat press for ten minutes under a condition of 70° C. and 2 MPa, theparticles are not formed into a film, that is, are not fused togetherbut are kept in the state of fine particles. The heat press used is sucha one that operates for pressuring a work under heating. The reason theabove conditions are used is that the fine particles that are not fusedtogether under the condition of 100° C. and 2 MPa tend to be detachedfrom the conductive particle 2, and that, if the fine particles that arefused together under the condition of 70° C. and 2 MPa are used as thefine particles of the insulating resin film, it may become difficult toform the voids A in the manner defined above. Meanwhile, the frictionalheat between the fine particles 3 a of the insulating resin and thatbetween the fine particles 3 a and the conductive particle 2 at the timeof collision between the fine particles 3 a and the conductive particle2 in the course of the processing of hybridization as later described ison the order of 80° C. under the conditions which will be set forthlater.

The conductive particle 1 carrying thereon an insulating film has thecontinuous insulating resin film 3 as the outer shell. This continuousinsulating resin film is formed by welding of fine particles 3 a of theinsulating resin. The outer shell covers the conductive particle 2 whichis the base particle 2 at least a surface of which is conductive. Theinsulating properties between the bumps is assured by the voids Abetween the neighboring fine particles 3 a. In addition, the insulatingresin film 3 of the outer shell is rendered breakable to assure the highinterconnection performance even with narrow-pitch bumps when theconductive particle 1 carrying thereon an insulating film is used in theanisotropic conductive interconnection material. That is, the conductiveparticle 1 carrying thereon an insulating film demonstrates superiorelectrical conductivity and insulating performance to achieve highinterconnection reliability.

With the conductive particle 1 carrying thereon an insulating film, thefine particles 3 a of the insulating resin used for forming theinsulating resin film 3 are formed of a material selected from the groupconsisting of a cross-linked acrylic resin, a styrene-acryl copolymer, adivinylbenzene-acryl copolymer, a styrene-divinylbenzene copolymer, amelamine-formaldehyde copolymer, a silicone-acryl copolymer, apolyamide, a polyimide, polybutadiene and NBR. It is thus possible toprovide the void A of the void ratio on the order of 19.1 to 38.1%between the neighboring fine particles of the insulating resin film 3.By coating the conductive particles 2 as the base particles with theinsulating resin film 3 presenting the preset voids A as describedabove, superior electrical conductivity and insulating performance maybe demonstrated even with narrow-pitch bumps to assure the facilitatedhighly reliable interconnection performance.

Further, with the anisotropic conductive interconnection material,provided with the conductive particle 1 carrying thereon the insulatingfilm, the conductive particle 1 carrying the insulating film thereon isdispersed within the insulating adhesive, as described above. It is thuspossible to maintain a facilitated interconnection performance and highconnection reliability even with narrow-pitch bumps.

The conductive particle 1 carrying thereon the insulating film accordingto the embodiment of the present invention is prepared by welding of thefine particles 3 a of the insulating resin film on the surface of theconductive particle 2 to form the insulating resin layer thereon byprocessing by a known hybridization system, sometimes referred to belowas ‘hybridization processing’. This hybridization processing compounds afine particle with another fine particle (see ‘Powder and Industry’,vol. 27, No. 8, 1995, p 35-42). With this processing, themechanical-thermal energy, consisting mainly of the force of impact, isimparted to a parent particle and a child particle dispersed in agaseous phase, thereby fixing the particles to form a film composed ofthe so fixed particles. Specified conditions for this hybridizationprocessing may suitably be determined in dependence upon the feedstockmaterial or an apparatus used.

The film thickness of the insulating resin film 3, formed to coat theconductive particle 2, and the voids between the fine particles formedwithin the insulating resin film 3, for producing the conductiveparticle 1 carrying thereon the insulating film by the hybridizationprocessing, have so far been described.

That is, the method for producing the conductive particle carryingthereon the insulating film according to the embodiment of the presentinvention includes a first step of forming the insulating resin film 3 cthat includes voids Ac in an initial state by colliding fine particles 3a of the insulating resin to a surface of conductive particle 2 as abase particle. The method also includes a second step of continuing thecollision of the fine particles 3 a to such an extent that the voids Acon a surface of the insulating resin film 3 c are decreased and thevoids Ac towards the base particle are maintained. At least the surfaceof the conductive particle as the base particle exhibits the electricalconductivity.

In the first step of this method, the above-described hybridizationprocessing is carried out for a preset time to form an initial-stateinsulating resin film 3 c that presents voids Ac on the surface of theinsulating resin film itself as well by the fine particles 3 a of theinsulating resin to collide with the surface of the conductive particle2, as shown in FIG. 3C.

In the second step, the hybridization processing is continued furtherfor a preset time to cause the fine particles 3 a of the insulatingresin to collide with the initial-state insulating resin film 3 cconstituting an outer shell of the base particle. This builds aninsulating resin film 3 shown in FIG. 3B in which the voids aredecreased to such an extent that there are no voids on the surface ofthe insulating resin film to render the surface uniform, and in whichthere are included voids A between neighboring fine particles within thebulk of the insulating resin film. By controlling the conditions of thehybridization at this time, it is possible to form the continuousinsulating resin film 3 in which there are included voids within thebulk of the insulating resin film between neighboring fine particles ata preset void ratio. However, the film also presents a continuoussurface based on welding of the fine particles. Specifically, bycontrolling the conditions of the hybridization for the first and secondsteps, such as rpm or time durations, it is possible to form suchinsulating resin film 3 in which larger numbers of voids A1 are includedin an inner part, with the number of voids A2 towards an outer partdecreasing to present a uniform smooth film state on the film surface.The insulating resin film has the voids at a preset void ratio.

If the hybridization processing is continued further for preset timefrom the state of FIG. 3B, a insulating resin film 103 shown in FIG. 3Ais formed. This film includes no voids and is uniform from the outersurface down to the innermost peripheral surface. Stated another way,the process of producing the conductive particle 1 carrying thereon aninsulating film according to the embodiment of the present invention iscontrolled in its production process to come to a close at a state inwhich the film includes the preset voids, that is, at a state short ofthat of forming the insulating resin film 103 which is uniformthroughout the film thickness. That is, such fine particles 3 a of theinsulating resin film 3, capable of forming the preset voids by thehybridization processing, are selected and used. On the other hand, thecondition of the hybridization is controlled so that preset voids willbe produced between the fine particles 3 a that also form the continuousinsulating resin film 3 to present a continuous smooth surface onwelding. By so doing, it is possible to form the insulating resin film 3that has a uniform surface state and that also presents voids at thepreset void ratio in such a manner that the insulating properties andthe electrical conductivity of the conductive particle 1 carryingthereon an insulating film will be demonstrated together.

The conductive particle 1 carrying thereon the insulating film, producedas described above, is then dispersed in an insulating adhesive toenable a paste-like or film-like anisotropic conductive interconnectionmaterial to be produced. The insulating adhesive used may be any one ofthose shown above.

The anisotropic conductive interconnection material that uses theconductive particle 1 carrying thereon the insulating film according tothe embodiment of the present invention may be sandwiched between twocomponents for connection, placed facing each other, such as between asemiconductor device and a substrate or between a flexible wiringsubstrate and a liquid crystal display device. The resulting assemblymay then be pressured under heating to yield an interconnectionstructure exhibiting an optimum conductive characteristic, an optimuminsulating characteristic and an optimum interconnection strength incombination.

That is, the conductive particle 1 carrying thereon the insulating filmaccording to the embodiment of the present invention includes thecontinuous insulating resin film 3 that is formed by welding of the fineparticles 3 a of the insulating resin and that covers the conductiveparticle 2 as the conductive base particle. There are formed largernumbers of voids A between the neighboring fine particles to assure theinsulation properties between the bumps. In addition, the insulatingresin film 3 of the outer shell is made susceptible to break to providefor facilitated reliable interconnection performance as well as highconnection reliability in interconnection even with narrow-pitch bumps.

The conductive particle carrying thereon an insulating film, accordingto the embodiment of the present invention, may be prepared by a methodincluding two steps. In a first step, an insulating resin film includinglarger numbers of voids in an initial state is formed by colliding thefine particles 3 a of the insulating resin to a surface of a conductiveparticle that exhibits electrical conductivity at least in its surface.In a second step, the collision of the fine particles is continued tosuch an extent that the voids on the surface of the insulating resinfilm are decreased and the voids towards the base particle aremaintained. This forms the conductive particle 1 carrying thereon aninsulating film, the inner part of which presents larger numbers ofpreset voids, as described above. That is, the conductive particle 1carrying thereon an insulating film, and which is used in theanisotropic conductive interconnection material that demonstrates asuperior electrical conduction characteristic and an optimum insulatingcharacteristic in establishing anisotropic conductive interconnectionbetween circuit components, may be produced. It is thus possible toprovide for facilitated interconnection as well as high interconnectionreliability even with narrow-pitch bumps.

The method for producing a conductive particle according to theembodiment of the present invention includes causing larger numbers offine particles of the insulating resin to collide with the surface ofthe base particle 2 to cause adhesion of the fine particles to thesurface of the base particle to coat the surface with the insulatingresin film. The insulating resin of the fine particle is selected fromthe group consisting of a cross-linked acrylic resin, a styrene-acrylcopolymer, a divinylbenzene-acryl copolymer, a styrene-divinylbenzenecopolymer, a melamine-formaldehyde copolymer, a silicone-acrylcopolymer, a polyamide, a polyimide, polybutadiene and NBR. At least thesurface of the base particle shows electrical conductivity. It is thuspossible to produce the conductive particle 1 carrying thereon aninsulating film, and which is used in the anisotropic conductiveinterconnection material that demonstrates a superior electricalconduction characteristic and an optimum insulating characteristic. Thisallows for establishing anisotropic conductive interconnection betweencircuit components. Moreover, it is possible to provide for facilitatedinterconnection as well as high reliability in the interconnection evenwith narrow-pitch bumps.

EXAMPLES

Certain Examples of the embodiment of the present invention are nowdescribed in detail. In the following description, Examples B1 to B4represent the Examples of the embodiment of the present invention. TheseExamples are in a state B that may be arrived at by the second step ofthe method of the embodiment of the present invention after a previousstate C that represents the first step. The previous state C is reachedby the first step of the method of the embodiment of the presentinvention and is such a state in which the film in its entirety issparse (see FIG. 3C). The state B is such a state in which a uniformsmooth surface is formed and the bulk of the film is sparse (see FIG.3B).

As Comparative Examples for comparison to the Examples of the embodimentof the present invention, Comparative Examples A1 to A3, which are in astate A having a film further formed commencing from the state B untilthe film is globally uniform in film thickness, are prepared (see FIG.3A). Comparative Examples C1 to C3 in the state C, in which the film issparse, as described above, are also prepared (see FIG. 3C). Evaluationwas conducted under the following conditions.

In the Examples B1 to B4, Comparative Examples A1 to A3 and C1 to C3,conductive particles, provided with insulating film shapes B, A and C,respectively, were prepared with variable insulating film thicknesses,with the particle sizes of the conductive particles, as the baseparticles, each being 5 μm. Each of the three sorts of the particles wasuniformly dispersed in an anionic curing epoxy adhesive material in aratio of 40 wt % of the particles to 100 wt % of the anionic curingepoxy adhesive material to form a film 25 μm in thickness for use as asample for evaluation. The fine particles of the insulating resin usedwere those of acrylic resin with variable particle sizes of 0.05, 0.2,0.5 and 0.7 μm. The conditions for hybridization for producing theinsulating film shapes A, B and C were 20 minutes with 16000 rpm forproviding the state A, 10 minutes with 16000 rpm for providing the stateB and three minutes for 16000 rpm for providing the state C.

As a specific evaluation method, an evaluation TEG for OCG was used, andthe electrical resistance as well as a gap when a short circuitgenerates of each of the above samples was measured under the conditionsas shown below. The gap when the short circuit generates was measuredfor evaluating the insulating properties.

To measure electrical conductivity, an IC for evaluation, shown in FIG.4, was used under the conditions as shown below. In FIG. 4, 31 denotesan IC chip, 32 denotes a bump, and 33 denotes an ITO (indium tin oxide)pattern (ITO pattern). 34 denotes a metal pattern in the IC chip (metalpattern in a chip). V and I denote a site for voltage measurement and asite for current application, respectively.

[IC Chip for Evaluation]

Bump Size: 30×85 μm; Pitch: 50 μm; Height h of the gold-plated bump(Au-plated bump): 15 μm

Glass plate for evaluation (Grass): pattern ITO, 10 Ω/cm², t=0.7 mm

Bonding condition: 190° C., 40 MPa and 5 sec

Insulation measurement was carried out as shown in FIG. 5 under theconditions as shown below. In FIG. 5, 42 denotes a bump, 43 denotes anITO pattern on a glass substrate and 44 denotes a metal pattern in an ICchip. R denotes a site for carrying out resistance measurement.

Bump Space: 15, 12.5, 10 and 7.5 μm; Bump Height: 15 μm

Bonding Condition: 190° C., 40 MPa and 5 sec

N=16 sets (10 points)/set

The electrical conductivity and the insulating property were measured onevaluation samples of the Examples B1 to B4 and Comparative Examples A1to A3 and C1 to C3, as described above. The results of evaluation areshown in Table 1, along with shapes of the insulating films and particlesizes of the fine particles of the insulating resins used.

TABLE 1 Conductor Particle spacing size of Insulat- Insulat- when ashort insulat- ing film ing film Electrical circuit ing fine Ex. Nos.shape thickness resistance generates particles Comparative A 0.05 μm  0.1Ω 12.5 μm  0.05 μm  Example A1 Comparative A 0.2 μm  0.5Ω 10 μm 0.2μm Example A2 Comparative A 0.5 μm  2.0Ω 10 μm 0.5 μm Example A3 ExampleB1 B 0.05 μm  0.05Ω 12.5 μm  0.05 μm  Example B2 B 0.2 μm 0.05Ω 10 μm0.2 μm Example B3 B 0.5 μm  0.1Ω 10 μm 0.5 μm Example B4 B 0.7 μm  0.3Ω7.5 μm  0.7 μm Comparative C 0.05 μm  0.05Ω 20 μm 0.05 μm  Example C1Comparative C 0.2 μm 0.05Ω 15 μm 0.2 μm Example C2 Comparative C 0.5 μm0.05Ω 15 μm 0.5 μm Example C3

With the Comparative Examples A1 to A3 of Table 1, the conductiveparticle A, having a uniform insulating resin film, free of voids, isprotected tightly by the insulating resin film, and hence exhibitssatisfactory conductor spacing when the short circuit generates.However, the particle A has a high value of the electrical resistance,which is not satisfactory with narrow-pitch bumps.

The conductive particles C, having larger numbers of voids but obtainedwith use of shorter hybridization time, according to the ComparativeExamples C1 to C3 of Table 1, are susceptible to peel-off. Although thevalues of the electrical resistance of the particles are satisfactory,the conductor spacing when the short circuit generates are longer.Hence, these particles are not desirable for use in narrow-pitch bumps.

With the Examples B1 to B4 of the embodiment of the present invention,in distinction from the above Comparative Examples, the insulating resinfilm exhibits larger numbers of preset voids on its inner peripheralsurface that coats a conductive resin film, while presenting acontinuous uniform outer peripheral film surface. In other words, thisinsulating resin film is provided with an inner insulating resin layerhaving larger numbers of preset voids and with an outer shell-likeinsulating resin layer. This may be achieved by controlling theconditions of hybridization, such as rpm or time, as later described indetail.

With the Examples B1 to B4, the insulating resin films are provided withlarger numbers of the inner voids and hence may be protected from beingpeeled off. The electrical resistance and the conductor spacing when theshort circuit generates are of values that may cope with narrow-pitchbumps. With the anisotropic conductive film, containing the conductiveparticles, it is possible to provide for facilitated interconnection ofnarrow-pitch bumps of the particle size of, for example, 30×85 μm andthe pitch on the order of 50 μm.

It is seen from the above-described Examples that the conductiveparticle provided with the insulating film of the present Example may beso formed that larger numbers of voids will be present in a proper statein the insulating resin film that coats the conductive particle. Thatis, the conductive particle has as its outer shell an insulating resinfilm that may cope with the narrow pitch bumps. This is made possible byjudiciously controlling the conditions of hybridization using theaforementioned fine particles operating as an insulating film.

With the conductive particle, provided with the insulating film,according to the embodiment of the present invention, it is possible toassure bump-to-bump insulating properties in contradistinction from theconductive particle that is uniform along the thickness of an insulatingresin film in related art. Moreover, the outer shell of the resin filmmay readily be cracked on pressuring due to the presence of the voids.The base particles on the bump may thus be readily collapsed to assureimproved connection reliability even with narrow-pitch bumps.

Thus, according to the embodiment of the present invention, theconnection reliability may be improved even with narrow-pitch bumps inthe anisotropic conductive circuit interconnection.

Although the present invention has so far been described with referenceto preferred embodiments, the present invention is not to be restrictedto the embodiments. It is to be appreciated that those skilled in theart can change or modify the embodiments without departing from thespirit and the scope of the present invention.

1. A conductive particle comprising: a base particle exhibitingelectrical conductivity at least on a surface thereof and a continuousinsulating resin film that covers said base particle; wherein saidinsulating resin film comprises: an inner insulating resin layer, whichis formed by fine particles adhering on the surface of said baseparticle with voids towards said base particle; and an outer shellinsulating layer formed continuously and uniformly at an outer surfaceof the insulting resin layer by welding of said fine particles.
 2. Theconductive particle according to claim 1 wherein a void ratiorepresenting a volume ratio of said voids to a total volume of saidinsulating resin film inclusive of said voids is in the range of 19.1 to38.1 percentage points.
 3. The conductive particle according to claim 1wherein said fine particles are formed of a material selected from thegroup consisting of a cross-linked acrylic resin, a styrene-acrylcopolymer, a divinylbenzene-acryl copolymer, a styrene-divinylbenzenecopolymer, a melamine-formaldehyde copolymer, a silicone-acrylcopolymer, a polyamide, a polyimide, polybutadiene and nitrile butadienerubber.
 4. An anisotropic conductive interconnection material comprisinga plurality of said conductive particles according to claim 1; saidconductive particles being dispersed in an insulating adhesive.
 5. Ananisotropic conductive interconnection material comprising a pluralityof said conductive particles according to claim 2, said conductiveparticles being dispersed in an insulating adhesive.
 6. An anisotropicconductive interconnection material comprising a plurality of saidconductive particles according to claim 3, said conductive particlesbeing dispersed in an insulating adhesive.
 7. The conductive particleaccording to claim 1, wherein the voids are formed at the inner surfaceof said insulating resin film adjacent the base particle.